Metal-organic frameworks (MOFs) are a class of hybrid materials comprising inorganic nodes and organic linkers. In many instances coordinatively unsaturated metal sites—either at the linkers or the nodes—are essential for engendering desired functional behavior. These sites can facilitate catalysis, gas storage, and gas separation.
MOFs have been metal-functionalized from the condensed phase (i.e., solution) either in de novo fashion or via post-synthesis modification. (See, Gordon, R. G.; Hausmann, D.; Kim, E.; Shepard, J. Chem. Vapor Depos. 2003, 9, 73.) Unfortunately, considerable effort (in the form of purification and activation) is necessary to ensure that excess metals, and/or undesired solvent and other reagents, are removed from solution-metallated MOFs. Solvent molecules can also irreversibly ligate otherwise coordinatively unsaturated metal sites, yielding, in turn, less-than-desirable materials properties.
Meilikhov et al. demonstrated that a variety of metal inclusion compounds (i.e., “metal@MOF” host-guest complexes) could be synthesized utilizing chemical vapor infiltration from volatile metal complexes under “sublimation-like” conditions. (See, Meilikhov, M.; Yusenko, K.; Esken, D.; Turner, S.; Van Tendeloo, G.; Fischer, R. A. Eur. J. Inorg. Chem. 2010, 3701.) However, little control can be obtained over the spatial distribution of the metal species within the MOF and, in some instances, the resulting metal@MOF structures are unstable.